Aqueous binder compositions

ABSTRACT

The invention relates to mixtures of at least one acrylic resin dispersion A and a second dispersion B which is at least one of a polyurethane dispersion B1 which comprises, in its polymer, moieties derived from grafted fatty acids, and a mixture B2 of a polyurethane dispersion B21 and an aqueously dispersed alkyd resin B22, and to a method of use thereof for coating of porous substrates.

FIELD OF THE INVENTION

The invention relates to aqueous binder compositions, to a process fortheir preparation, and to a method of use thereof.

BACKGROUND OF THE INVENTION

Aqueous binders have been used for a variety of purposes, particularlyfor the preparation of coating compositions, adhesives, and impregnants.In these applications, the binders have various functions, such assealing of pores in a porous substrate, or film formation on the surfaceof a substrate, which film may serve as protective layer or asfunctional layer such as adhesion layer, decorative layer, reflectivelayer, thermally insulating layer, or layer with certain electric ormagnetic properties.

The chemical nature of the binder is decisive for the adhesion,mechanical, and chemical properties of the film or layer formed. Whilethere is a certain range of properties available for a specific chemicalsystem by modification of the basic polymer, determined by the kind ofpolymer formed in the crosslinking reaction that leads to a solid filmor layer, it is frequently desired to be able to tailor the propertiesof the polymers formed in the crosslinking reaction in a way ofcombining e.g. the gloss of an alkyd resin, the lightfastness of analiphatic polymer such as aliphatic acrylate copolymers, the corrosionprotection of an epoxy resin system, the scratch resistance ofsilicones, and the mechanical and chemical resistance of polyurethanes.

STATE OF THE ART

Combinations of aqueous dispersions of polyurethane resins and ofacrylic resins have been described in EP 0 350 157 A2. These dispersionsare made from an aqueous polyurethane dispersion, an aqueous acrylicresin dispersion, and a further dispersion made by radicallypolymerising a mixture of acrylic monomers in the presence of thefirst-mentioned polyurethane resin dispersion. The polyester polyol usedin this document may made by reacting an unsaturated carboxylic acidwith a glycol component, which embodiment provides a functional bondbetween with the radically polymerisable acrylic monomers. If hydrazineis used for chain extension of the polyurethane, reaction of thehydrazine groups with carbonyl or carboxamido group of the acrylicpolymer occurs during or after film formation. As hydrazine presents anenvironmental and toxicological problem, however, such systems cannot beused broadly.

A base-coat composition comprising an aqueous acrylic resin and aurethane resin emulsion has been known from EP 0 379 158 A2. An aqueousacrylic resin is admixed to a urethane resin emulsion, wherein theacrylic resin has an acid number of from 20 mg/g to 150 mg/g, and anumber-average molar mass of from 5 kg/mol to 30 kg/mol. The urethaneresin is made by reacting in a solvent an aliphatic or alicyclicdiisocyanate, a polyether diol or a polyester diol, a low molar masspolyhydroxy compound, and a dimethylolalkanoic acid, neutralisation anddispersing in water, under chain extension with water, and optionally,removal of the solvent. The two resins are mixed in a ratio of the massm_(A) of acrylic resin to the mass m_(U) of polyurethane resin, the massin each case being the mass of the solid resin, of from 12/88 to 1/99 asit had been found that the water resistance is impaired if the massfraction of the acrylic resin exceeds 12%, and that the pigments addedto the mixed dispersion are not held stably in a dispersed state if themass fraction of acrylic resin is reduced to below 1%. The base coat iscured together with a clearcoat, with an isocyanate crosslinker.

In EP 0 421 609 A2, a water-based acrylic coating composition isdisclosed the binder of which comprises mass fractions of from 60% to90% of an acrylic copolymer and from 10% to 40% of a polyurethane. Theacrylic copolymer is made in an emulsion polymerisation process andcomprises mass fractions of from 1% to 10% of moieties derived from oneor both of methylol methacrylamide and methylol acrylamide.

Aqueous coating compositions comprising an acrylic copolymer and aurethane oligomer dispersion are also described in EP 0 458 243 A1. Theacrylic copolymer has a number-average molar mass of from 6 kg/mol to 50kg/mol, and has amide groups, acid groups, and hydroxyl groups, and theurethane oligomer is derived from a hydroxyl group terminated diol, adiisocyanate compound, active hydrogen-containing hydrophilic compounds,and the prepolymer made therefrom is neutralised and chain-extended inan aqueous medium comprising primary or secondary polyamines. The massfraction of the acrylic copolymer in the binary mixture is from 95% to10%, the mass in each case being the mass of the solid resin. Themixture of the two resin dispersions is crosslinked with amelamine-formaldehyde resin.

In EP 0 580 163, an aqueous coating composition is disclosed whichcomprises an acrylic resin emulsion, and a urethane emulsion, acrosslinking agent, and an acidic phosphate or phosphite ester. Theacrylic resins have an acid number of from 20 mg/g to 150 mg/g and anumber-average molar mass of from 5 kg/mol to 30 kg/mol. The urethaneemulsion is made by first synthesising a urethane prepolymer from analiphatic or cycloaliphatic diisocyanate, a polyether diol or polyesterdiol having a number-average molar mass of from 500 g/mol to 5 kg/mol, alow molar mass polyhydroxyl compound, and a dimethylol alkanoic acid.This prepolymer is mixed with water after or during neutralisation ofthe prepolymer with a tertiary amine, and the resulting mixture ischain-extended by water. The organic solvent used during the prepolymerformation is then distilled off. Melamine formaldehyde resins and phenolformaldehyde resins are useful as crosslinkers. The ratio of the massm_(A) of acrylic resin to the mass m_(U) of urethane resin is between 90kg/10 kg to 60 kg/40 kg, and the ratio of the sum of the mass m_(A) ofacrylic resin and the mass m_(U) of urethane resin to the mass m_(C) ofcrosslinker resin (m_(A)+m_(U))/m_(C) is between 95 kg/5 kg and 60 kg/40kg, masses of resins always being the mass of the solid resin present inthe emulsion or dispersion. The acidic phosphate or phosphite ester hasthe general formula HO—P(O)(OR¹)(OR²) or HO—P(OR¹)(OR²).

A water-based coating composition the binder of which comprises anacrylic silane copolymer with an acid number of from 2 mg/g to 100 mg/gand a hydroxyl number of up to 100 mg/g, a glass transition temperatureof from −40° C. to 25° C. and a weight average molar mass of from 500kg/mol to 3000 kg/mol, and a polyurethane which may be a polyesterurethane, a polyether urethane, or a polyacrylourethane, comprisingmoieties derived from a compound having groups that are reactive withisocyanate groups, and groups capable of forming an anion. In theacrylic copolymer, moieties derived from a silane acrylate ormethacrylate of formula(R¹O)(R²O)R Si—CH₂—(CH₂)—CH₂—O—CO—C(R³)═CH₂is present in a mass fraction of from 1% to 10%. These coatingcompositions are used as base coats which are cured at ambienttemperature for twenty-one days.

In EP 1 435 370 A1, a coating composition is disclosed which comprisesan emulsion of an acrylic copolymer, an aqueous urethane resin, a waxemulsion, an alkaline soluble resin, and a UV absorber. The resins areonly defined in very general terms, by reciting monomers that may beused, and by reference to trade names in the examples with noexplanation of composition nor values of characteristic parameters.

A three-coat one-bake film forming method is disclosed in EP 1 477 236A1 where onto an electrodeposited coating film, an intermediate paint, abase paint, and a clear paint are applied one after the other, and curedby application of heat after the last layer has been applied. Theintermediate paint comprises a urethane-modified polyester resin havinga number average molar mass of from 1.5 kg/mol to 3 kg/mol, a melaminecrosslinker resin, a blocked isocyanate where the blocking agent has anactivated methylene group, and a non-aqueous dispersion of an acrylicresin having a core-shell structure.

An aqueous paint composition which is used in formation of amultilayered film has been disclosed in EP 1 852 478 A1, where thesecond aqueous paint of three consecutively-applied paint layers iscomprised of an emulsion polymer of a monomer mixture which comprises across-linking vinyl monomer a carboxyl group-containing vinyl monomer, ahydroxy group-containing vinyl monomer, and further polymerisable vinylmonomers, a water-soluble acrylic resin which contains amide groups, aurethane emulsion and a curing agent, wherein the first-named emulsionpolymer has a core-shell structure. Hybrid resins for airbag coatingsare known from EP 1 887 060 A1, which hybrid resins are urethanesblended with acrylate resins, vinyl resins, silicone resins, andcombinations thereof, at least one of the components having a glasstransition temperature of 20° C. or less. The urethanes are preferablyof the polycarbonate, polytetramethylene glycol, silicon-based diol, orolefin-based diol type, and are made from these components together withan aliphatic diisocyanate and a carboxylic or sulphonic acid also havingtwo hydroxyl groups. These resins are said to form an interpenetratingnetwork.

Aqueous coating compositions having a mixture of a urethane based resin,a chlorinated polyolefin resin, and optionally, also an acrylic-basedresin, have been described in EP 1 958 995 A2. All resins are describedin very general terms. While the polycarbonate based polyurethane resinused in the examples is identified not only by trade name, but also byelongation at break and tensile strength of a film made therefrom,measured on a non-specified sample with a non-specified test method, theacrylic based resin is only identified by a trade name.

An aqueous primer composition has been disclosed in EP 2 009 071 A1.This primer comprises a modified polyolefin dispersion, an aqueousurethane resin and/or aqueous acrylic resin, a conductive metal oxide,and aluminium flakes. The urethane resin is described in thespecification in very general terms, and no specific information can bedrawn from the examples as the urethane resin is only identified by itstrade name.

None of the cited documents discloses combinations of polyurethaneresins, acrylic resins and alkyd resins. There is also no suggestion ofincorporating an alkyd resin moiety or oil-based moiety into apolyurethane resin and admixing this modified polyurethane resin to anacrylic resin dispersion.

SUMMARY OF THE INVENTION

It has been found in the experiments that have led to the presentinvention that combinations of polyurethane resins, alkyd resins, andacrylic resins, in the form of their aqueous dispersions, and, in thealternative, combinations of polyurethane resins comprising moietiesderived from grafted fatty acids, with acrylic resins, both in the formof their aqueous dispersions, lead to binders for coating compositionshave a desirable combination of application properties with theadvantageous features of all components.

The invention therefore relates to mixtures of at least one acrylicresin dispersion A and a second dispersion B which is at least one of apolyurethane dispersion B1 which comprises, in its polymer, moietiesderived from grafted fatty acids, and a mixture B2 of a polyurethanedispersion B21 and an aqueously dispersed alkyd resin B22.

The invention further relates to a process of making mixtures of atleast one acrylic resin dispersion A and a second dispersion B, and to amethod of use of these mixtures to prepare binders for coatingcompositions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The acrylic dispersion A preferably has a minimum film formingtemperature of less than 35° C., corresponding to a glass transitiontemperature of up to 30° C., a hydroxyl number of from 0 mg/g to 50mg/g, and an acid number of from 2 mg/g to 25 mg/g, which are made byemulsion copolymerisation of at least two olefinically unsaturatedmonomers A1 and A2. Usually, at least one of the olefinicallyunsaturated monomers A1 and A2 is an acrylate or a methacrylate whichgives the name of “acrylic dispersion” to A. The acrylic dispersions Apreferably have particle sizes from 50 nm to 300 nm, particularlypreferably from 70 nm to 250 nm, and especially preferred, from 90 nm to180 nm. The mass fraction of solids in the dispersions is preferablyfrom 33% up to 55%.

The monomers A1 are selected from the group consisting of olefinicallyunsaturated monomers that have no functional group other than olefinicdouble bonds, i. e. those monomers that are free from hydroxyl groups,amino groups, mercapto groups, epoxide groups, and acid groups, whichmonomers A1 are selected from the group consisting of esters A11 ofolefinically unsaturated carboxylic acids with monohydroxy compoundssuch as aliphatic linear branched, or cyclic alcohols, of olefinicallyunsaturated aromatic compounds A12 having at least one olefinicallyunsaturated aliphatic substituent on an aromatic residue derived fromoptionally substituted aromatic compounds by removal of a hydrogen atombonded to an aromatic ring, of olefinically unsaturated esters A13 of anunsaturated aliphatic alcohol and a saturated aliphatic carboxylic acid,of ethers A14 of the formula R¹—O—R², wherein both R¹ and R² are linearor branched aliphatic radicals having from one to twenty carbon atoms,and at least one of R¹ and R² is olefinically unsaturated in which casethe number of carbon atoms is at least two, of unsaturated aliphaticketones A15 of the formula R³—CO—R⁴, wherein both R³ and R⁴ are linearor branched or cyclic aliphatic radicals having from one to twentycarbon atoms, and at least one of R³ and R⁴ is olefinically unsaturatedin which case the number of carbon atoms is at least two, and ofunsaturated aliphatic halogenides and nitriles A16 of the formula R⁵—Xwhere X is F, Cl, Br, I, or CN, and R⁵ is an unsaturated aliphaticradical having from two to twenty carbon atoms, where it is alsopossible that more than one hydrogen atom of the olefinicallyunsaturated aliphatic compound R⁵—H are substituted by atoms or groupsX.

Preferred monomers A11 are esters of olefinically unsaturated carboxylicacids with aliphatic alcohols having from one to twenty carbon atoms,particularly, methyl (meth)acrylate, ethyl (meth)acrylate, the isomericpropyl (meth)acrylates, the isomeric butyl (meth)acrylates, 2-ethylhexyl(meth)acrylate, decyl (meth)acrylate, tridecyl (meth)acrylate, andstearyl (meth)acrylate, where (meth)acrylate stands for either acrylateor methacrylate. Other useful monomers A11 are diesters of olefinicallyunsaturated dicarboxylic acids with aliphatic alcohols having from oneto twenty carbon atoms, such as diesters of maleic, fumaric, itaconic,citraconic and mesaconic acids, with methanol, ethanol, butanol, n- andisopropanol, n-, iso-, sec.- and tert.-butanol, 2-ethylhexanol, decanol,tridecanol and stearylalcohol, as well as mixed esters of these.

Preferred monomers A12 are dimethyl maleinate, diethyl maleinate,dimethyl fumarate, and diethyl fumarate.

Preferred monomers A13 are vinyl and allyl esters of aliphatic linear orbranched monocarboxylic acids such as vinyl acetate, vinyl propionate,vinyl 2-ethylhexanoate, vinyl neopentanoate, vinyl pivalate, and vinylneodecanoate, and the commercially available mixture of vinyl esters ofalpha-branched decanoic acids (“®Versatic acid”) as well as theanalogous esters of allyl and methallyl alcohols.

Preferred monomers A14 are styrene, the isomeric mixture of vinyltoluenes, 4-vinyl pyridine, and 2-vinylnaphthalene.

Preferred monomers A15 are ethers of vinyl and of allyl alcohols withsaturated aliphatic linear or branched alcohols having from one totwenty carbon atoms such as methyl vinyl ether, ethyl vinyl ether, n-and iso-butyl vinyl ether, methyl allyl ether, and propyl allyl ether.

Preferred monomers A16 are olefinically unsaturated ketones,particularly ketones that have one vinyl or allyl group, and one linearor bached or cyclic aliphatic group having from one to twenty carbonatoms, such as methyl vinyl ketone, ethyl vinyl ketone, and n-propylvinyl ketone.

The monomers A2 have additional functionalities next to beingolefinically unsaturated, which functionalities are preferably selectedfrom the group consisting of acid, hydroxyl, and acid amide, where theacid functionalities may be carboxylic acid —COOH, sulphonic acid-SO₂OH,sulphuric acid —O—SO₂OH, phosphonic acid —PO(OH)₂, phosphoric acid—O—PO(OH)₂, and the acid amide functionalities may be those of thecorresponding amides.

One group of monomers A21 which belong to group A2 are acid-functionalolefinically unsaturated monomers which have at least one acid groupwhich may preferably be a carboxylic acid group, —COOH, a sulphonic acidgroup —SO₃H, a sulfinic acid group —SO₂H, and a phosphonic acid group—PO(OH)₂. Useful monomers A21 are acrylic acid, methacrylic acid, maleicacid, fumaric acid, the half esters of maleic or fumaric acid, vinylsulphonic acid, vinyl phosphonic acid, and allyloxy hydroxypropylsulphonic acid, as well as salts of these.

Another group of monomers A22, which belong to the group A2 arehydroxyalkyl esters of the monomers listed in the group A21, such ashydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, andhydroxybutyl (meth)acrylate.

Another group of monomers A23, which belong to the group A2 are acidamides based on the acid monomers A21 such as (meth)acrylamide,N,N-dimethyl (meth)acrylamide and homologues thereof.

Further optional monomers are the monomers A3 that contribute toimproving the adhesion of coatings prepared with the acrylic copolymerscomprising these optional monomers to substrates coated. These optionalmonomers A3 are olefinically unsaturated and carry additional groupswhich may be trialkyl silane groups, trialkoxysilane groups, mixedalkyl/alkoxysilane groups, ureido groups, beta-keto acid groups, orbeta-hydroxy acid groups. Particularly preferred are vinyltrimethoxysilane, vinyl dimethoxymethylsilane, vinyltris(2-methoxyethoxy)-silane,(methacryloxymethyl)-methyldimethoxysilane, trimethoxysilane(meth)acrylate, 2-ethyl (2-oxoimidazolidin-1-yl) methacrylate, 2-ethyl(2-oxoimidazolidin-1-yl) (meth)acrylate, acetoacetoxyethyl(meth)acrylate, beta-ketoglutaric acid vinyl ester, andbeta-hydroxybutyric acid allyl ester.

The mass fraction of moieties derived from monomers A1 in the polymer A,calculated as the ratio of the mass m_(A1) of monomers A1 and the massm_(A) of the polymer A, is preferably from 80% to 99.5%, particularlypreferably, from 85% to 99%. The mass fraction of moieties derived frommonomers A2 in the polymer A, calculated as the ratio of the mass m_(A2)of all monomers of group A2 present in the monomer mixture and the massm_(A) of the polymer A, is preferably from 0.5% to 20%, particularlypreferably, from 1% to 15%. The mass fraction of moieties derived frommonomers A3 which are optionally also present in the polymer A,calculated as the ratio of the mass m_(A3) of monomers A3 and the massm_(A) of the polymer A, is preferably from 0.1% to 7%, particularlypreferably, from 0.5% to 5%, and especially preferred, from 1% to 4%.

The minimum film forming temperature (MFT) of the polymer A, as measuredin accordance with DIN 53787 and DIN 53 366 (ISO 2115) is preferablybetween −5° C. and 35° C. In a preferred embodiment, the MFT may be inthe range of from 0° C. to 20° C.

The abbreviation “(meth)acryl” stands for either or both of acryl andmethacryl.

The second aqueous dispersion B is at least one of a polyurethanedispersion B1 which comprises, in its polymer, moieties derived fromoils or alkyd resins, or both, and a mixture B2 of a polyurethanedispersion B21 and an aqueously dispersed alkyd resin B22.

The aqueous polyurethane dispersion B1 comprises in its polymer a moietyderived from a polyfunctional isocyanate, a moiety derived from at leastone polyhydric alcohol having at least two hydroxyl groups, a moietyderived from at least one fatty acid, and a moiety derived from ahydroxyfunctional compound made from a grafted fatty acid which in turnis made from a fatty acid having at least one olefinic unsaturation, andgrafted with a mixture of olefinically unsaturated monomers whichmixture comprises at least one acid-functional olefinically unsaturatedmonomer, wherein the grafted fatty acid has on average at least 1.1 acidgroups per molecule. This aqueously dispersed polyurethane B1 ispreferably made in a multi-step reaction, where in the first step, afatty acid having at least one olefinic unsaturation is grafted with amixture of olefinically unsaturated monomers which mixture comprises atleast one acid-functional olefinically unsaturated monomer, to provide agrafted fatty acid having on average at least 1.1 acid groups permolecule, in the second step, a compound which is hydroxy-functional ismade by reacting with the said grafted fatty acid at least onepolyhydric alcohol having at least two hydroxyl groups, at least onefatty acid, and optionally, at least one polyfunctional acid having atleast two acid groups, and/or an anhydride thereof, and in the thirdstep, a polyurethane is made by reacting the hydroxy functional compoundwith a polyfunctional isocyanate, and optionally, a low molar masspolyhydric alcohol having a molar mass of up to 2000 g/mol and at leasttwo hydroxyl groups per molecule, and further optionally, a polymericpolyol having at least two hydroxyl groups per molecule, and which isderived from a polyester, a polyacrylate, a polycarbonate, a polyether,or an olefin polymer and further optionally, a dihydroxyalkanoic acidhaving a sterically hindered acid group where the carbon atom carryingthe carboxyl group is a tertiary or quaternary carbon atom. In a furtherstep, the product of the third step is reacted with at least one chainextender, having at least two functional groups that react withisocyanate groups, and optionally, at least one of monofunctionalcompounds also referred to as chain stoppers that have only one groupthat is reactive towards isocyanate groups, and of compounds that haveat least two different kinds of groups that have different reactivitytowards isocyanate groups, selected from the group consisting of primaryhydroxyl groups —CH₂OH, secondary hydroxyl groups >CH(OH), tertiaryhydroxyl groups >C(OH)—, primary amino groups —NH2, secondary aminogroups >NH, and mercapto groups —SH, which are used to impart additionalfunctional groups into the polyurethane.

In the reaction of the third step between the hydroxy functionalcompounds and the poly-functional isocyanate, the stoichiometry has tobe selected in a way to make a polyurethane, i. e. the amount ofsubstance n(—NCO) of isocyanate groups in the polyfunctional isocyanatehas to be at least 0.9 of the sum of the amounts of substance n(—OH) ofhydroxyl groups in the hydroxyfunctional compounds employed in the thirdstep, in other words, the ratio n(—NCO)/n(—OH) 0.9 mol/mol, butpreferably not more than 1.3 mol/mol. Preferably, this ration(—NCO)/n(—OH) is at least 1.05 mol/mol, and with particular preference,at least 1.1 mol/mol. An excess of isocyanate groups is also needed inorder to add a chain-extension step, as is well known to a personskilled in the art.

The mixture B2 of a polyurethane dispersion B21 and an aqueouslydispersed alkyd resin B22 is obtained by mixing an aqueous polyurethanedispersion B21 and an aqueous dispersion of an alkyd resin B22.

Preferably, the aqueous polyurethane dispersion B21 has a mass fractionof solids of from 30% to 65%, a hydroxyl number of from 20 mg/g to 200mg/g, corresponding to an average hydroxy functionality a) of at least1.8 in the polyurethane molecules, b) a mass fraction of —NH—CO— groups(molar mass=43.02 g/mol) in the polyurethane of from 5% to 25%, c) aspecific content of chemically incorporated anionic groups in thepolyurethane of from 0 mmol/hg to 200 mmol/hg and d) a mass fraction ofethylene oxide units (molar mass=44.05 g/mol) of from 0% to 25%, in thepolyurethane, which are incorporated within terminal and/or lateralpolyether chains within the polyurethane, wherein either the groups c)or the groups d), or both, are chemically bound within the polyurethanein an amount which is sufficient to maintain the polyurethane stablydispersed in water. Preferably, a polyurethane dispersion as describedas B1 is used.

Preferably, the aqueously dispersed alkyd resin B22 is as described inU.S. Pat. No. 4,333,865A1, especially preferred, that of U.S. Pat. No.6,489,398 B1, particularly preferred that described in example A3 of thelatter.

The mixtures according to the invention of at least one acrylic resindispersion A and a second dispersion B which is at least one of apolyurethane dispersion B1 which comprises, in its polymer, moietiesderived from grafted fatty acids, and a mixture B2 of a polyurethanedispersion B21 and an aqueously dispersed alkyd resin B22 can be usedwith preference to formulate coating compositions for wood and otherporous materials such as paper, cardboard, leather, textiles, andconcrete, but also plastics, glass, and metals.

Preferably, the mixtures comprise mass fractions of from 20% to 70% ofacrylic resins A, and 80% to 30% of the polymer of the second dispersionB, where masses are always the mass of the solid resin present in thedispersion. In the case of B1, the mass fraction of moieties derivedfrom grafted fatty acids in the polyurethane is preferably from 12% to40%, particularly preferably from 15% to 35%, and especially preferred,from 20% to 30%. In the case of B2, the mass fraction of the alkyd resinin the sum of the mass of alkyd resin and polyurethane resin ispreferably from 30% to 80%, particularly preferably from 40% to 70%, andespecially preferred, from 50% to 60%.

The mixtures can be applied to substrates as is, or may be mixed withadditives such as flow or levelling additives, defoamers, wettingagents, as well as with dyestuffs or pigments. Addition of commonly usedsiccatives such as those based on lead, cobalt or manganese, optionallyin mixture with calcium, barium or zirconium salts, acceleratescross-linking by air-drying.

Mixtures according to the invention lead to good wood penetration, fastdrying, low water spot formation propensity, and reduced dirt pick-upwhen used for wood coating.

Particularly good results have been obtained when mixtures have beenmade of aqueous dispersions of acrylic resins A and aqueous dispersionsof the second polymer B, where the preferred compositions and ranges ofparameters as claimed in the dependent claims have been combined.

EXAMPLES Example 1 Preparation of an Acrylic Resin

800 g of deionised water were charged into a mixing vessel. A mixture of102 g of an emulsifier (sodium salt of a fatty alcohol ether sulphate,Disponil® FES 32 P, Cognis GmbH), and a monomer mixture comprising 400 gof styrene, 400 g of methyl methacrylate, 900 g of butyl acrylate, 270 gof a solution comprising 67.5 g of 2-ethyl (2-oxoimidazolidin-1-yl)methacrylate and 202.5 g of methyl methacrylate, and 30 g of acrylicacid were added and stirred to form a homogeneous emulsion. A reactorwas charged with 1600 g of deionised water and 12.2 g of the emulsifiermentioned supra, the contents were well stirred, and heated to 80° C.under a nitrogen blanket. An initiator solution comprising 36 g of waterand 4 g of ammonium peroxodisulphate was added under stirring, and then,the monomer pre-emulsion was added over five hours. The reaction mixturewas then held at 80° C. for one further hour, and then cooled to 60° C.Residual monomers were consumed by adding a further initiator solutionof 1.14 g of tert.-butyl hydroperoxide and 6.68 g of water, and asolution of a reducing agent (1 g of the sodium salt of hydroxymethanesulfinic acid with 19 g of water) during thirty minutes ofpost-reaction. The reaction mixture was then cooled to 30° C. andneutralised by adding 16 g of a 25% strength solution of ammonia inwater (25 g of NH₃ in 100 g of the solution). The resulting dispersionof acrylic resin had a viscosity (measured at 23° C. and 100 s⁻¹) of 200mPa·s, a mass fraction of solids of 44%, a pH of 8.4, and a mass averageof particle size of 110 nm.

Example 2 Preparation of an Oxydatively Drying Polyurethane Resin

2.1 (Grafted Fatty Acids)

71 g of linseed oil fatty acid were charged in a reactor and heated to140° C. A monomer mixture consisting of 55 g of isobutyl methacrylate,10 g of para-methyl styrene and 35 g of methacrylic acid together with 4g of di-tert. butyl peroxide was added continuously over eight hours.The mixture was kept at 140° C. thereafter until a conversion to polymerof at least 99% had been reached, as witnessed by the mass fraction ofsolids measured. Finally, the reaction mixture was diluted with xylene.The solution had a mass fraction of solids of 75%, and an acid number of203 mg/g.

2.2 (Polyol)

270 g of pentaerythritol, 150 g of phthalic anhydride and 1000 g of soybean oil fatty acid were charged to a reactor and heated to 250° C. Themixture was kept under esterification conditions, viz., at a constanttemperature of 250° C. under removal of water by azeotropic distillationwith xylene until an acid number of approximately 4 mg/g or lower hadbeen reached. The reactor was then cooled down to approximately 170° C.,and 1000 g of the grafted fatty acid mixture of example 1 were chargedto the reactor. The mixture was heated up to 205° C. and stirred at thistemperature until the mixture was transparent (about twenty minutes).The reaction mixture was then cooled down to 170° C., and residualxylene was removed by distillation under reduced pressure until a massfraction of solids of at least 99% had been reached. The mixture waskept at 170° C. under stirring until the final acid number of 50 mg/gwas reached and then cooled down. The hydroxyl number of this polyol wasin the range of from 36 mg/g to 44 mg/g when repeating this example,with an average of 40 mg/g.

2.3 (Polyurethane)

375 g of the polyol of example 2.2 were charged into a vessel togetherwith 273 g of tetramethyl meta-xylylene diisocyanate (TMXDI) and heatedto 90° C. The resulting reaction mixture was stirred at that temperatureuntil the isocyanate concentration (mass fraction of isocyanate groupsin the reaction mixture) was 1.5%. The prepolymer was cooled to 80° C.,and 24.5 g of triethylamine were added. After fifteen minutes ofhomogenisation, 374 g of warm (40° C.) water were added within fiveminutes and subsequently to that, a mixture of 2.7 g of hydrazine and 47g of water were added. The product was stirred for two hours at theresulting temperature and after that the formation of a polyurethanedispersion with a mass fraction of solids of 48% was complete. Thedispersion had an acid number of 45 mg/g, a pH of a 10% strengthdispersion in water of 8.8, a mass average particle size of 130 nm, anda dynamic viscosity of 900 mPa·s (measured at 23° C. and a shear rate of10 s⁻¹).

Example 3 Mixture of Polyurethane and Alkyd Resin

3.1 Synthesis of a Polyurethane

A mixture of 132.8 g of a polyester diol prepared from phthalicanhydride and hexanediol having a hydroxyl number of 56 mg/g, 5.0 g of apolyether monohydric alcohol having a hydroxyl number of 26.2 mg/g andprepared from n-butanol, and a mixture of 83 mol of ethylene oxide and17 mol of propylene oxide, 13.4 g of neopentylglycol, 20.6 g of2,2-dimethylolpropionic acid, and 90 g of N-methylpyrrolidinone washeated to 70° C. under stirring. To this mixture, 127.6 g of4,4′-dicyclohexylmethane diisocyanate were added, and the resultingmixture was stirred and heated at 110° C. for one hour until thetheoretical isocyanate content was reached. The reaction mixture wascooled to 70° C., and 15.6 g of triethylamine were added. After stirringfor 15 minutes at 70° C., 17.0 g of ethanolamine and 50 g ofN-methylpyrrolidinone were added. After the reaction mixture had reached92° C. due to the exothermic reaction, the mixture was cooled to 70° C.and stirred until no more free NCO groups could be detected by infraredspectroscopy. 5.0 g of the above polyether monohydric alcohol in 50 g ofN-methylpyrrolidone were then added, and the reaction mixture wasstirred for thirty minutes. 391.3 g of distilled water with atemperature of 50° C. were added to the mixture, and the resultingdispersion was stirred for one hour. The following data were found: a pHof 9.3, a mass fraction of solids of 35%, an average hydroxyfunctionality per molecule of 2, and a mass fraction of NH—CO groups of13%.

3.2 Synthesis of a Urethane-Modified Alkyd Resin

200 g of the grafted fatty acid of Example 2.1 were charged to areactor, together with 67 g of trimethylol propane, and 140 g ofsunflower oil fatty acid, and heated to 175° C. The mixture was keptunder esterification conditions at a constant temperature of 175° C.under removal of water by azeotropic distillation with xylene until anacid number of approximately 65 mg/g had been reached. All solvent wasthen removed by distillation under reduced pressure. Within thirtyminutes, 55 g of toluylene diisocyanate were added at 70° C., thetemperature slowly rising due to the exothermic reaction to 100° C. Atthis temperature, the reaction was continued until a Staudinger index of8.5 cm³/g had been reached. Additional diisocyanate was added if therewas need, when repeating this experiment, care being taken that noresidual free isocyanate was left after reaching the desired value ofthe Staudinger index. Then, the solid resin was emulsified by adding 610ml of water and 15 g of an aqueous ammonia solution of 25% strength,yielding an aqueous emulsion of the binder with a mass fraction ofsolids of 40%, a dynamic viscosity measured at 23° C. and a shear rateof 10 s⁻¹ of 3500 mPa·s, an average particle size of 120 nm, an acidnumber of 52 mg/g, and a pH of 8.8, measured at 10% strength in water.

3.3 Preparation of a Mixture of Polyurethane and Alkyd Resin

445 g of the polyurethane dispersion of example 3.1 and 555 g of theurethane-modified alkyd resin dispersion of example 3.2 were stirred forthirty minutes in a resin kettle. A homogeneous dispersion was obtained.

Example 4 Application Test

4.1 Mixture of the Polyurethane Dispersion of Example 2 and AcrylicResin Dispersion of Example 1

300 g of the acrylic dispersion of example 1 and 700 g of thepolyurethane dispersion of example 2 were mixed in a resin kettle understirring until a homogeneous dispersion was obtained.

4.2 Mixture of the Polyurethane/Alkyd Dispersion of Example 3 andAcrylic Resin Dispersion of Example 1

300 g of the acrylic dispersion of example 1 and 700 g of the mixedpolyurethane/alkyd dispersion of example 3 were mixed in a resin kettleunder stirring until a homogeneous dispersion was obtained.

4.3 Acrylic-Modified Alkyd Resin Dispersion (Comparative)

An alkyd resin dispersion was made according to example 1.3, resindispersion B1, of U.S. Pat. No. 5,698,625.

4.4 Application Test Results

The dispersions according to examples 4.1, 4.2, and 4.3 (comparative)were formulated into paints P1, P2, and P3 by adding, to 56 g each ofthe dispersions, 1.8 g of a red pigment (Pigment Red 101), 1.7 g of ayellow pigment (Pigment Yellow 42), 0.04 g of a black pigment (PigmentBlack 7/77266), and 38 g of water. In the case of paints P1 and P2, 0.6g of a water-emulsifiable combination drier free of nonylphenolethoxylate comprising organic salts of cobalt, lithium, and zirconiumwas added, and 0.9 g of the same drier was added to paint 4.3.

These paints were applied in two coats with drying (7 days) after eachapplication to pressure treated pine having a residual humidity of lessthan, or equal to, a mass fraction of water of 5%. In the first coat, awet film thickness of 107 μm (380 sq ft/gal) was applied, dried for 7days, and then, the second coat with a wet film thickness of 73 μm (560sq ft/gal) was applied, and dried again for 7 days.

Chemical resistance against vinegar, and household bleaching agents wasOK in all cases, on singly coated pine (7 days drying). The dry time wasdetermined as the time when no colour was removed after blotting thecoating at the specified time:

P1 P2 P3 (comp.) Dry time - 1st coat 9 min 12 min 13 min Dry time - 2ndcoat. 9 min 11 min 18 min Residual tack After Drying 4 4 2 Residual Tackafter ninety minutes 4 4 2

Tack was judged according to the following list: 0: sticky; 1: strongtack; 2: tack; 3: mild tack; 4: very mild tack; 5: no tack

Additional to the fast drying behaviour found with both inventive paintsP1 and P2 compared to P3, a significant and unexpected improvement wasfound in the dirt pick-up behaviour where two coats of paints P1, P2 andP3 each were applied to pressured-treated pine, each layer having beendried for 7 days. The coated boards were then preheated to 104° F. (40°C.), and a red iron oxide slurry was applied in a wet film thickness of73 μm (560 sq ft/gal) and let stand for four hours, whereafter theslurry was washed away with water and a brush, and the surface judgedvisually (5: no damage; 4: very mild damage; 3: mild damage; 2: damageand mild discolouration; 1: damage and strong discolouration; 0: strongdamage). Paint P1 had a rating of 4 to 5, paint P2 had a rating of 3,and paint P3 (comparative) had a rating of 2.

These data confirm that the binder mixtures according to the inventionshow very satisfactory and unexpected results particularly for the useas deck stain.

The invention claimed is:
 1. A process for the preparation of mixturesof at least one acrylic resin dispersion A and a second dispersion B,where B is at least one of dispersion B1 and dispersion B2, where saiddispersion B1 is a polyurethane dispersion comprising, in its polymer,moieties derived from grafted fatty acids which grafted fatty acids haveat least 1.1 acid groups per molecule, and said dispersion B2 is amixture of a polyurethane dispersion B21 and an aqueously dispersedalkyd resin B22, the process comprising the following steps: preparingat least one of said dispersion B1 and said dispersion B2, wherein thedispersion B1 is prepared in a multi-step reaction where in a firststep, a fatty acid having at least one olefinic unsaturation is graftedwith a mixture of olefinically unsaturated monomers which mixturecomprises at least one acid-functional olefinically unsaturated monomer,to provide a grafted fatty acid having on average at least 1.1 acidgroups per molecule, in a second step, a compound which ishydroxy-functional is made by reacting with the grafted fatty acid atleast one polyhydric alcohol having at least two hydroxyl groups, and atleast one fatty acid, and in a third step, a polyurethane is made byreacting the hydroxy functional compound with a polyfunctionalisocyanate wherein the ratio n(—NCO)/n(—OH) of the amount of substancen(—NCO) of isocyanate groups in the polyfunctional isocyanate to the sumof the amounts of substance n(—OH) of hydroxyl groups in thehydroxyfunctional compounds employed in the third step is at least 1.05mol/mol, and in a further step, the product of the third step is reactedwith at least one chain extender having at least two functional groupsthat react with isocyanate groups, and wherein the dispersion B21 isprepared in a multi-step reaction where in a first step, a fatty acidhaving at least one olefinic unsaturation is grafted with a mixture ofolefinically unsaturated monomers which mixture comprises at least oneacid-functional olefinically unsaturated monomer, to provide a graftedfatty acid having on average at least 1.1 acid groups per molecule, in asecond step, a compound which is hydroxy-functional is made by reactingwith the grafted fatty acid at least one polyhydric alcohol having atleast two hydroxyl groups, at least one fatty acid, and optionally, atleast one polyfunctional acid having at least two acid groups, and/or ananhydride thereof, and in a third step, a polyurethane is made byreacting the hydroxy functional compound with a polyfunctionalisocyanate wherein the ratio n(—NCO)/n(—OH) of the amount of substancen(—NCO) of isocyanate groups in the polyfunctional isocyanate to the sumof the amounts of substance n(—OH) of hydroxyl groups in thehydroxyfunctional compounds employed in the third step has to be atleast 1.05 mol/mol, and in a further step, the product of the third stepis reacted with at least one chain extender having at least twofunctional groups that react with isocyanate groups to yieldpolyurethane dispersion B21 which has a mass fraction of solids of from30% to 65%, a hydroxyl number of from 20 mg/g to 200 mg/g, a specificcontent of chemically incorporated anionic groups of from 0 mmol/hg to200 mmol/hg, and a mass fraction of ethylene oxide units of from 0% to25% which are incorporated within terminal or lateral polyether chainswithin the polyurethane, preparing a mixture of the dispersion B21 andthe aqueously dispersed alkyd resin B22 to obtain the dispersion B2, andmixing the at least one acrylic resin dispersion A and at least one ofthe second dispersions B1 and B2 to obtain a mixture.
 2. The process ofclaim 1 wherein the mixtures comprise mass fractions of from 20% to 70%of acrylic resins present in the at least one acrylic resin dispersionA, and 80% to 30% of the polymer of the second dispersion B, wheremasses are always the mass of the solid resin present in the dispersion.3. The process of claim 1 wherein the polymer of the second dispersion Bis the polymer of the polyurethane dispersion B1 which comprises a massfraction of moieties derived from grafted fatty acids in thepolyurethane of from 12% to 40%, where masses are always the mass of thesolid resin present in the dispersion.
 4. The process of claim 1 whereinthe polymer of the second dispersion B is a mixture of the polymerspresent in dispersion B2 which is a mixture of the polyurethane resinpresent in the polyurethane dispersion B21 and of the alkyd resinpresent in the aqueously dispersed alkyd resin B22, and wherein the massfraction of the alkyd resin in the sum of the mass of alkyd resin andpolyurethane resin is from 30% to 80%.
 5. The process of claim 4 whereinthe aqueously dispersed alkyd resin B22 comprises moieties derived fromgrafted fatty acids, and wherein the mass fraction of moieties derivedfrom grafted fatty acids in the dispersion B2 is from 12% to 40%, wheremasses are always the mass of the solid resin present in the dispersion.6. The process of claim 1 wherein the acrylic resin dispersion A has aminimum film forming temperature of less than 35° C., corresponding to aglass transition temperature of up to 30° C., a hydroxyl number of from0 mg/g to 50 mg/g, and an acid number of from 2 mg/g to 25 mg/g, whichare made by emulsion copolymerisation of at least two olefinicallyunsaturated monomers A1 and A2.
 7. The process of claim 6 wherein themonomers A1 are selected from the group consisting of olefinicallyunsaturated monomers A1 selected from the group consisting of esters A11of olefinically unsaturated carboxylic acids with monohydroxy compoundssuch as aliphatic linear branched, or cyclic alcohols, of olefinicallyunsaturated aromatic compounds A12 having at least one olefinicallyunsaturated aliphatic substituent on an aromatic residue derived fromoptionally substituted aromatic compounds by removal of a hydrogen atombonded to an aromatic ring, of olefinically unsaturated esters A13 of anunsaturated aliphatic alcohol and a saturated aliphatic carboxylic acid,of ethers A14 of the formula R¹—O—R², wherein both R¹ and R² are linearor branched aliphatic radicals having from one to twenty carbon atoms,and at least one of R¹ and R² is olefinically unsaturated in which casethe number of carbon atoms is at least two, of unsaturated aliphaticketones A15 of the formula R³—CO—R⁴, wherein both R³ and R⁴ are linearor branched or cyclic aliphatic radicals having from one to twentycarbon atoms, and at least one of R³ and R⁴ is olefinically unsaturatedin which case the number of carbon atoms is at least two, and ofunsaturated aliphatic halogenides and nitriles A16 of the formula R⁵—Xwhere X is F, Cl, Br, I, or CN, and R⁵ is an unsaturated aliphaticradical having from two to twenty carbon atoms, where it is alsopossible that more than one hydrogen atom of the olefinicallyunsaturated aliphatic compound R⁵—H are substituted by the atoms orgroups X.
 8. The process of claim 6 wherein the monomers A2 haveadditional functionalities next to being olefinically unsaturated, whichfunctionalities are selected from the group consisting of acid,hydroxyl, and acid amide, where the acid functionalities are carboxylicacid —COOH, sulphonic acid-SO₂OH, sulphuric acid —O—SO₂OH, phosphonicacid —PP(OH)₂, phosphoric acid —O—PO(OH)₂, and the acid amidefunctionalities are those of the corresponding amides.
 9. The process ofclaim 1 wherein, in the dispersion B2 which is the mixture of thepolyurethane dispersion B21 and the aqueously dispersed alkyd resin B22,the aqueous polyurethane dispersion B21 has a mass fraction of solids offrom 30% to 65%, a hydroxyl number of from 20 mg/g to 200 mg/g,corresponding to an average hydroxy functionality a) of at least 1.8 inthe polyurethane molecules, b) a mass fraction of —NH—CO— groups,calculated with a molar mass of from 43.02 g/mol, in the polyurethane offrom 5% to 25%, c) a specific content of chemically incorporated anionicgroups in the polyurethane of from 0 mmol/hg to 200 mmol/hg and d) amass fraction of ethylene oxide units, calculated with a molar mass offrom 44.05 g/mol, of from 0% to 25%, in the polyurethane, which areincorporated within terminal and/or lateral polyether chains within thepolyurethane, wherein either the groups c) or the groups d), or both,are chemically bound within the polyurethane in an amount which issufficient to maintain the polyurethane stably dispersed in water. 10.The process of claim 1 wherein a siccative is added to the mixture ofthe at least one acrylic resin dispersion A and the second dispersion B.11. A method of use of the mixtures obtained by the process of claim 1to prepare a coating composition by admixing a siccative, and at leastone of pigments, defoamers, levelling agents, antisettling agents,antiskinning agents, and sag control agents, and applying the coatingcomposition to a substrate selected from the group consisting of wood,leather, paper, cardboard, concrete, and plaster.